Marathon Monday was a day of celebration for Krystle Campbell, just like it was for everyone else in Boston. She and a friend joined the euphoric crowd on Boylston Street to watch thousands of exhausted runners make their final strides over the finish line. They cheered. And then a pair of explosions tore through the throng, taking lives and limbs in a rain of shrapnel.

Roughly 24 hours after two pressure-cooker bombs exploded Monday afternoon at the Boston Marathon, officials publicly identified 29-year-old Campbell of Arlington, Mass., as one of three fatalities in what President Obama called a “heinous and cowardly act.” The two other victims were Martin Richard, 8, and Lu Lingzi, a graduate student from China studying statistics at Boston University.

The preceding day had been full of uncertainty and grief for the victims and their loved ones, especially Campbell’s. Word that she was missing quickly spread among her family, but according to the Associated Press, the misidentification of her friend, who was severely injured in the attack, led Campbell’s parents to believe their daughter had lived while her friend had died. It wasn’t until hospital staff showed them the patient that they realized the magnitude of their loss

Born in Somerville, Campbell graduated from Medford High School in 2001. Roy Belson, the school district’s superintendent said, “From what I can gather from talking to everybody, she was a very energetic, likeable woman who had strong convictions.” After studying at the University of Massachusetts Boston, Campbell found work in management and catering at Jasper White’s Summer Shack, a local chain of seafood restaurants. The company posted a statement on its website calling her an “inspiration to all of us.”

Campbell moved to Arlington about a year ago and recently began working as a manager at Jimmy’s Steer House on Massachusetts Avenue. It’s the kind of place where people stop in for a rare steak, a stiff drink and quality service. Shena Parent, 25, a front-of-house manager there, said she and Campbell had started around the same time and formed a quick bond.

“She basically took me underneath her wing,” Parent said. Campbell introduced her to the back-of-house staff, taught her some of the basics and helped her build rapport with other employees. “She was the first one there if you needed something.”

Donna Grenier, a server at Jimmy’s for 27 years, said it took Campbell no time to “fit in like a glove here.” Grenier had trained her one-on-one for a week and said Campbell’s “wonderful” service made customers and colleagues enjoy her company. “She was going to go places.”

On Tuesday afternoon, Parent began alerting staff that Campbell appeared to be a victim of the attack. She planned to individually meet with each employee, but the news flashed across television screens in the bar before she got the chance. After that, the restaurant was inundated with calls from other staffers: “Tell me it’s not her. It’s not really her, right?” they asked Parent. “My heart went in my throat. I couldn’t believe it,” she said. “This just hit way too close to home.”

Later in the day, a gaggle of television cameras and reporters grouped in front of the Campbell family’s white-sided house on Park Street in Medford. Stepping up to the microphones on her wooden porch, Campbell’s mother, Patty, gave a brief statement: “Krystle Marie, she was a wonderful person. Everybody that knew her loved her,” she said. “I can’t believe this has happened.”

Campbell’s father, William, told a reporter that she was the “most lovable girl. She helped everybody, and I’m just so shocked right now.” Her grandmother, Lillian, spoke with the Boston Globe about a conversation she had with William: “You know, it’s not right. My granddaughter shouldn’t die before me.”

As her family and friends slip from shock into sadness, Campbell is being remembered as a fiercely loyal hard-worker with immense pride for her city. “She was the best,” her mother said. “You couldn’t ask for a better daughter.”